1. Field of the Invention
The present invention relates to the technology of preventing the congestion of cells in a cell-switching device of a synchronous transfer mode (ATM) switching device, etc.
2. Description of the Related Art
A large number of organizations have been studying ATM switching technology to realize the broadband integrated services digital network (ISDN) of the coming generation. In the ATM switching device, the contents of subscriber information (data, voice images, . . . ) are switched through a packet of a fixed length called a cell. As a result, the ATM system can transfer information at a high speed.
A calling acceptance judgment algorithm based on a band value declared by the user has been studied in order to make the most of the multiple effects of the utilization of the resources in the ATM switch.
The more the multiple effect is utilized, the more easily the cell congestion occurs in the network (switch). Therefore, an effective congestion preventing technology is required when a cell congestion occurs in operating the ATM switch.
According to the conventional technology for preventing congestion, a cell receiving terminal unit (destination terminal unit) is notified of the congestion, when the congestion is detected in the network, by setting the explicit forward congestion indication (EFCI) having the value of 101 or 011 is set in the 3-bit payload type (PT) field of the cell which has caused the congestion.
However, the above described prior art has the problem that the congestion cannot be properly controlled if the destination terminal unit does not have the function of detecting the EFCI, and that the terminal unit (source terminal unit) which has sent the congestion causing cell is not notified of the congestion.
Furthermore, the above described prior art has the problem that the congestion cannot be properly controlled if there is a long duration between the occurrence of the congestion and the start of the control because of the delay of cells in the transmission line and the delay of the processes performed in each terminal even if the destination and source terminals have functions mentioned above.